As a device for measuring inner diameter of a hollow member or a hollow shaft, a device is disclosed in the Patent Document 1 is known, for instance.
In the inner diameter measuring device as disclosed in the Patent Document 1, a pipe to be inspected is rotatably supported by a pipe rotating and supporting device, and there is provided a running carriage where a pair of inner diameter measuring units at upper and lower positions are provided and where a pair of inner diameter measuring units can be brought closer to each other or can be separated from each other. By running the running carriage, the inner diameter measuring units are inserted into the pipe to be inspected, and the inner diameter measuring units are separated to upper and lower positions and the inner diameter measuring units are brought into contact with an inner surface of the pipe to be inspected. Further, the pipe to be inspected is rotated by the pipe rotation supporting device, and an inner diameter of the pipe to be inspected is measured.
The inner diameter measuring device as described above is designed in such complicated structure that the pipe rotation supporting device has a driving unit to rotate the pipe, that the running carriage is traveled and that a pair of inner diameter measuring units is moved up and down. Further, there is a problem in that inner diameter of a pipe to be inspected with a length longer in axial direction cannot be measured because the measurement of inner diameter is restricted within such a range as far as the inner diameter measuring unit can be inserted.
Therefore, when a measurement is performed on inner diameter of a pipe to be measured with longer length over total axial length, such structure is required that the inner diameter measuring unit can be inserted from a base end to a forward end into the pipe to be measured. Further, a moving direction must coincide with a center line of the pipe to be measured.
To solve the problems as described above, it is an object of the present invention to provide an inner diameter measuring device, by which to easily align the center line of the pipe to be measured with the moving direction of the inner diameter measuring unit with respect to the pipe to be measured and to measure the inner diameter over the entire axial length of the pipe to be measured.